A two-channel microspectrofluorometer (Biochem. Biophys., Acta, 286; 189, 1972) and a modified multichannel microspectrofluorometer (Biochem. Biophys, Acta, 362; 575, 1974) allow the correlated study of intracellular metabolic interactions and intercellular communication (e.g., the junctional transfer of fluorescent molecules and metabolites) in conjunction with electrophysiological techniques. At the intracellular level, a multisite microtopographic study of metabolic interactions (e.g., the responses or local asynchronicites of NAD and NAD(P)-linked pathways to substrate microinjected by microelectrophoresis) is made from 50-200 regions of an EL2 ascites cell simultaneously at a temporal resolution of 32-64 msec. At the intercellular level, the transfer of fluorescent molecules (fluorescein, 1-N-etheno-adenosine 3-5 cyclic phosphate, dansyl lysine) from a cell microinjected with such probes to its neighbors (e.g., within a few hundred millisec to a few sec) is followed (e.g., in Chironomus salivary gland cells or Chang liver cells). Subtle changes in cell-to-cell coupling (e.g., changes in the rate of junctional flow or selective passage for a certain form or size of molecule) are amenable to study in correlation with intracellular metabolic processes or their alterations by drugs or pathology.